The SQUID is one of the most sensitive magnetic field devices in the prior art, and it can be used for wide range of applications, including biology, medicine, geology, systems for semiconductor circuit diagnostics, security, magnetic resonance imaging (MRI) and even cosmology research. In recent years, arrays of coupled oscillators have been considered as a general mechanism for improving signal detection and amplification. Theoretical and experimental studies can be interpreted to show that arrays of SQUIDs can yield comparable improvements in signal output relative to background noise, over those of a single SQUID device.
A peculiar configuration that has gained considerable attention among the physics and engineering community is that of multi-loop arrays of Josephson Junctions (JJs) with non-uniformly distributed loop areas. Typically, each loop contains two JJs, i.e., a standard DC-SQUID, but the loop size varies from loop to loop. These types of unconventional geometric structures of JJs are known to exhibit a magnetic flux dependent voltage response V(φe), where φe denotes an external magnetic flux normalized by the quantum flux, that has a pronounced single peak with a large voltage swing at zero magnetic field. The potential high dynamic range and linearity of the “anti-peak” voltage response render the array an ideal detector of absolute strength of external magnetic fields. These arrays are also commonly known as Superconducting Quantum Interference Filters (SQIFs).
Improving the linearity of SQIFs is critical for developing advanced technologies, such as low noise amplifiers (LNA's) that can further increase link margins and affect an entire communication system. SQIFs can also be used in unmanned aerial vehicles (UAVs), where size, weight and power are limited, and as “electrically small” antennas to provide acceptable gain for the antenna. SQIFs can also be used in land mine detection applications. But for all of these applications, it is desired to improve the linear response of the SQIF device.
The quest to increase the linearity of SQUID and SQIF arrays was boosted by the introduction of the bi-SQUID, which has three 3 JJ's. A non-linear inductance of the additional third JJ can provide a desired linearizing effect for the orverall SQIF. These bi-SQUIDs are now being used in uniform and non-uniform (SQIF) arrays in place of conventional dc SQUIDs with a goal of achieving higher linearity. However, most of the design efforts to date that use SQUIDs and/or bi-SQUIDs are directed at the optimization of one-dimensional (1D) serial or parallel arrays and their combinations. This is due to the higher complexity analysis and modeling required for 2D arrays to account for mutual coupling that occurs between neighboring cells and complex current distribution in arrays. What is desired is a two-dimensnional array of bi-SQUIDs.
In view of the above, it is an object of the present invention to provide a two-dimensional (2D) SQIF array having a tightly coupled 2D network of bi-SQUID cells, in which junctions and inductances are shared between adjacent bi-SQUID cells. Another object of the present invention is to provide a two-dimensional (2D) SQIF array having diamond shaped, dual bi-SQUID cells. Still another object of the present invention is to provide a 2D SQIF that maximizes the number of bi-SQUID cells which can be placed with a given SQIF array area. Yet another object of the present invention is to maximize the voltage response and dynamic range of a SQIF by manipulating the critical current, inductive coupling between loops, number of loops, bias current, and distribution of loop areas of the array cells of diamond bi-SQUIDs. Still another object of the present invention is to provide a 2D SQIF array with increased high dynamic range and linearity of the “anti-peak” response, for use in multiple applications such as magnetic field detectors, magnetic antennas and wide-band low-noise amplifiers. Another object of the present invention is to provide a SQIF and methods for manufacture that can be easily tailored in a cost-effective manner to result in a SQIF having bi-SQUID array cells that has been optimized according to the user's needs.